Crystalline microporous and mesoporous metal silicates and use thereof

ABSTRACT

Microporous and mesoporous metal silicates are prepared by the hydrothermal reaction of a silicon and metal source in the presence of a template. The choice of raw materials influences the purity and hence the catalytic activity of the products. A pyrogenic mixed oxide is used as the silicon and metal source. Prepared products have the composition (SiO 2 ) 1−x (A m O n ) x , where A is Ti, Al, B, V or Zr and x is 0.005 to 0.1. Shaped objects of the microporous and mesoporous metal silicates are obtained directly by using a shaped object of the pyrogenic mixed oxide. The products obtained are used as oxidation catalysts.

REFERENCE TO A RELATED APPLICATION

[0001] This is a divisional application based on copending applicationSer. No. 08/878,509 filed Jun. 19, 1998 which is relied on andincorporated herein by reference.

INTRODUCTION AND BACKGROUND

[0002] The present invention relates to a process for the preparation ofcrystalline microporous and mesoporous metal silicates composed ofsilicon dioxide and one or more metal oxides. In another aspect, thepresent invention relates to products obtainable by said process. Stillfurther, the present invention relates to the use of these products.

[0003] A variety of crystalline microporous and mesoporous metalsilicates are known. According to the IUPAC definition, micropores areunderstood as meaning pores with a diameter of less than 2 nm, andmesopores are understood as meaning pores with a diameter of 2 to 50 nm.These definitions are used herein.

[0004] Some crystalline metal silicates with regular micropores ormesopores are extremely effective catalysts in a very wide variety ofapplications. In particular, microporous products of the composition(SiO₂)_(1−x)(TiO₂)_(x), in which titanium atoms replace some of thesilicon atoms in the crystal lattice, have achieved industrialimportance as oxidation catalysts. The structures of these metalsilicates differ according to the starting materials and conditions ofpreparation. Thus, for example, so-called titanium silicalite-1,titanium silicalite-2 and titanium beta-zeolite have the MFI, MEL andBEA crystal structures, respectively. Crystal structure types of knownzeolites and silicalites are described in W. M. Meier, D. H. Olson,Atlas of Zeolite Structure Types, Butterworth-Heinemann, 1993. Knownstructures with regular mesopores are the MCM-41 and MCM-48 structuresdescribed in C. T. Kresge et al., Nature, 359 (1992), pp. 710-712. Asurvey of structures with regular mesopores is also given in S. Behrens,Angew, Chemie, 1996, 108 (5), pp. 561-564.

[0005] It is known that the catalytic efficacy of generic metalsilicates is substantially dependent on their phase purity and themorphology and, hence, on the conditions of preparation. For example,the catalytic activity of titanium silicalite is reduced by othertitanium-containing phases, for instance TiO₂, and by an increase in thecrystal size; see, B. Notari in (a) Catal. Today 18 (1993), p. 163 and(b) Stud. Surf. Sci. Catal., 67 (1991), p. 243.

[0006] Generic metal silicates, for instance titanium silicalite-1, canbe prepared by hydrothermal synthesis. In the first step, a siliconsource and a titanium source, conventionally tetraalkyl orthosilicateand tetraalkyl orthotitanate, and water are condensed to a gel in thepresence of a structure-determining quaternary ammonium cation, usuallyused in the form of the quaternary ammonium hydroxide, and the gel isthen crystallized under hydrothermal conditions, usually above 100°C.and under autogenous pressure. The solid formed is separated off,washed, dried and calcined above 300°C. The way in which the Ticomponent is introduced is liable to cause problems, it often beingimpossible to exclude contamination of the product by TiO₂ as a foreignphase—loc. cit. B. Notari (b). According to EP 543 247, the quaternaryammonium hydroxide can be replaced as the template with a combination ofa quaternary ammonium salt and a base such as ammonia, although thecrystals obtained are relatively large. According to U.S. Pat. No.5,198,203 a mesoporous titanium silicate of the MCM-41 structure can beprepared with cetyltrimethylammonium hydroxide as the template.

[0007] Another known silicon source is pyrogenic silicic acid. Accordingto R. Kumar et al. in Stud. Surf. Sci. Catal., 84 (1994) p. 109,titanium silicalite-1 can be obtained by hydrothermal synthesis frompyrogenic silicic acid and tetrabutyl orthotitanate. The use of atetraalkyl orthotitanate carries the risk of obtaining a product ofinsufficient phase purity.

[0008] According to EP 0 311 983, titanium silicalites are prepared byimpregnating a coprecipitated porous TiO₂—SiO₂ material, which can beamorphous or crystalline, with a template compound and then subjectingthe product to hydrothermal synthesis. Suggestions of usingcoprecipitates with other metals, or pyrogenic mixed oxides, are not tobe found in said document.

[0009] In known synthesis processes the generic microporous metalsilicates are formed as crystallites with a size usually of less thanone micrometer, which can only be separated from a liquid atconsiderable expenses. For many industrial applications the finematerial is therefore coarsened by a subsequent agglomeration step.According to EP 0 265 018, the agglomeration is effected usingoligomeric SiO₂ as a binder.

[0010] According to EP 0 299 430, a preformed amorphus SiO₂ matrix isimpregnated with an aqueous solution containing a soluble titaniumcompound and a suitable template, and crystallized under hydrothermalconditions, the shape and size of the SiO₂ matrix remaining essentiallyunchanged. This process again has the disadvantage that the use of asoluble titanium compound carries the risk of reducing the phase purityand hence the catalytic activity.

[0011] Accordingly, it is an object of the invention to produce genericmetal silicates of high phase purity and high catalytic activity.

[0012] Another object of the invention is to provide a process suitablenot only for the preparation of products based on(SiO₂)_(1−x)(TiO₂)_(x), but also for the preparation of products inwhich titanium is replaced with one or more other metals in the crystallattice.

[0013] Still further, another object of the invention is to carry outthe process in such a way that binder-free shaped objects of thecrystalline microporous and mesoporous metal silicates can be obtaineddirectly, i.e., without a subsequent agglomeration step.

SUMMARY OF THE INVENTION

[0014] In achieving the above and other objects, a feature of theinvention resides in a process for the preparation of microporous andmesoporous metal silicates, comprising the hydrothermal reaction of asilicon source in the presence of a metal source and a template whereina pyrogenic metal-silicon mixed oxide is used as the silicon and metalsource. Any suitable template can be used for purposes of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The general composition of the pyrogenic mixed oxides and hencealso of the crystalline microporous and mesoporous metal silicates to beprepared is represented as follows:

(SiO₂)_(1−x)(A_(m)O_(n))_(x)   (Ia),(SiO₂)_(1−x)((A_(m)O_(n))_(1-y)(A′_(m),O_(n),)_(y))_(x)   (Ib).

[0016] In the above formulae, A and A′ are each the same or differentmetal of valency p selected from the group consisting of:

[0017] B, Al, Ga, In, Ge, Sn and Pb or from subgroups 3 to 8 of thePeriodic Table of Elements;

[0018] m and m′ and n and n′ are the number of atoms, where m·p=2n andm′·p=2n′;

[0019] x is a number from 0.0001 to 0.25, preferably from 0.001 to 0.2and especially from 0.005 to 0.1; and

[0020] y in formula (Ib) is a number greater than 0 and less than 1.

[0021] Apart from SiO₂, pyrogenic mixed oxides which are preferably tobe used contain one or more oxides selected from the group consisting ofAl₂O₃, B₂O₃, TiO₂, ZrO₂, V₂O₅, Cr₂O₃ and Fe₂O₃. Oxides of the subgroupelements are optionally present not only in the highest oxidation statebut also in a lower oxidation state. Generic metal silicates which areto be used as oxidation catalysts are prepared with mixed oxides whichare free of aluminum oxide, the process according to the inventiongiving metal silicalites in this case. Generic metal silicates of thecomposition

(SiO₂)_(1−x)(M_(r)A_(m)O_(n),)   (II)

[0022] are prepared using mixed oxides of composition (Ia). M incomposition (II) is a cation of valency q selected from the groupconsisting of alkali metals, alkaline earth metals, H⁺, NH₄ ⁺andN(alkyl)₄ ⁺; m·p+r·q=2n″ in (II). In the process according to theinvention, M is introduced into the metal silicate either via thetemplate or via alkali metal or alkaline earth metal hydroxide orammonia present in the hydrothermal synthesis. After the calcination ofa generic metal silicate of composition (II), M is a proton or an alkalimetal or alkaline earth metal ion. However, said cations M or othercations can also be incorporated into the microporous and mesoporousmetal silicates at a later stage by means of conventional ion exchangereactions.

[0023] The pyrogenic mixed oxides to be used in the process according tothe invention can be prepared in a manner known per se from a mixture ofa volatile silicon compound and one or more volatile metal compounds(compounds of A and/or A′), for example, by flame hydrolysis or theluminous arc process. The process according to the invention ispreferably carried out using pyrogenic mixed oxides of silicon whichhave been prepared by flame hydrolysis, for example, those known fromUllmann's Encyklopädie der Technischen Chemie (Ullmann's Encyclopedia ofChemical Technology), 4th edition, vol. 21, pp. 464-465 (1982) and DE-A36 11 449.

[0024] The process according to the invention can be carried out usingboth the pulverulent pyrogenic mixed oxides and shaped objects thereof.

[0025] The shaped objects of the metal-silicon mixed oxide can beproduced by known processes, for example, spray granulation, fluidizedbed granulation, extrusion, pelleting or tableting. In a preferredembodiment of the invention the shaped objects can be produced by meansof spray granulation, as described, for example, in DE-A 36 11 449.

[0026] In the process according to the invention the pyrogenicmetal/silicon mixed oxide, in powder form or in the form of abinder-free shaped object produced therefrom, is brought into contactwith an aqueous solution of a suitable template; when using coarsershaped objects of mixed oxide, for instance extrudates, this isconventionally an impregnation process. After intermediate drying, ifappropriate, this step is followed by the hydrothermal reaction toconvert the pyrogenic metal-silicon mixed oxide to the crystallinemicroporous or mesoporous metal silicate according to the invention.After the hydrothermal reaction, the template is removed from the metalsilicate in a manner known, per se, conventionally by extraction or,preferably by calcination.

[0027] Suitable template compounds are amines having one or more aminogroups, amino alcohols or tetrasubstituted ammonium compounds.Tetraalkylammonium compounds are particularly suitable, especiallytetraalkylammonium hydroxide. The nature of the alkyl groups in saidtetraalkylammonium compounds is significant in terms of the porestructure. The tetraalkylammonium compounds used to prepare microporousmetal silicates according to the invention are preferably those in whichalkyl is ethyl, propyl and butyl, preferably n-propyl. Thus, forexample, metal silicates according to the invention of the MFI, MEL andBEA structure can be prepared using tetra-n-propylammonium,tetra-n-butylammonium and tetraalkylammonium compounds, respectively.The tetraalkylammonium compounds used to prepare mesoporous metalsilicates according to the invention are preferably those which havesurfactant properties. Accordingly, these compounds contain an alkylgroup or an alkenyl group having at least 7 C atoms in the longestchain. Particularly preferred ammonium compounds are those of thegeneral formula RNR′₃ ⁺X⁻, in which R contains 12 to 18 C atoms and ispreferably unbranched and saturated, R′ has 1 or 2 C atoms, and X is theanion, conventionally hydroxide or halide. Cetyltrimethylammoniumchloride or bromide and lauryltrimethylammonium chloride or bromide areparticularly suitable for the preparation of mesoporous structures. Whenusing tetraalkylammonium halides as the template, a base, such asammonia, a primary, secondary or tertiary amine or an alkali metal oralkaline earth metal hydroxide, is added to the template solution usedfor the contacting/impregnation process. The template compound isconventionally used in a molar ratio of template to SiO₂ of 0.05 to 2.0.For the preparation of microporous metal silicates, a molar ratiotemplate to SiO₂ of from 0.05 to 1.0, especially from 0.10 to 0.45, ispreferred. For the preparation of mesoporous metal silicates accordingto the invention of the MCM-41 or MCM-48 structure, a molar ratio oftemplate to SiO₂ of from 0.05 to 2.0, especially of from 0.1 to 0.8, ispreferred.

[0028] The molar ratio OH/SiO₂ is generally from 0.05 to 2.0 andpreferably from 0.1 to 1.0. In the hydrothermal reaction to the molarratio H₂O/SiO₂ is from 1 to 200 and preferably from 4 to 100. Seedcrystals of the same structural type can be added to the reactionmixture if necessary. The molar ratio H₂O/SiO₂ is generally lower whenusing shaped objects of pyrogenic mixed oxides than when using pyrogenicmixed oxides as obtained directly by flame hydrolysis.

[0029] In the process according to the invention for the preparation ofmicroporous metal silicates, the hydrothermal reaction is conventionallycarried out under autogenous pressure at a temperature from 100 to200°C. and preferably from 150 to 190°C. Mesoporous metal silicatesaccording to the invention can also be prepared at lower temperature,the conventional temperature range being from 25 to 200°C., preferablyfrom 50 to 175°C. and especially from 70 to 150°C. The hydrothermalreaction is carried out until the pyrogenic mixed oxide used has beencompletely converted to the crystalline microporous or mesoporous metalsilicate according to the invention at the given reaction temperature.The degree of completion of the reaction can be determined by knownmethods of structural analysis. Under optimized conditions the reactiontime is conventionally from 1 to 50 hours.

[0030] To remove the template compound from the solid obtained in thehydrothermal reaction, said solid is usually calcined at from 300 to1000°C., optionally after a prior washing process, it being possible forthe calcination step to include a shaping process at the same time. Inthe case of the mesoporous metal silicates according to the invention,at least some of the template compound can also be removed by extractionwith an organic solvent.

[0031] In one particular embodiment of the process according to theinvention, the pyrogenic metal-silicon mixed oxide, for instance asobtained by flame hydrolysis, is suspended in an aqueous templatesolution. The molar ratios used here can be the same as those indicatedabove. This suspension is spray-dried, and the resulting granulescontaining the template are treated in an autoclave at elevatedtemperature, for example, at 175°C., optionally in a steam atmosphere.The spray drying is advantageously carried out by setting thetemperature of the drying air in the range of 100 to 500°C. so that theresulting granules have a water content of 5 to 50 wt. %. After thehydrothermal reaction, the shaped objects obtained are calcined at atemperature of 300 to 1000°C., preferably of 400 to 800°C., to removethe template.

[0032] The process according to the invention can be carried outreproducibly and is easy to control. The use of the pyrogenic mixedoxides avoids problems due to the presence of foreign phases of themetal oxides in question. A high catalytic activity is a characteristicfeature of the crystalline microporous and mesoporous metal silicatesobtainable by the process according to the invention. The generic metalsilicates can moreover be obtained not only in the form of very finelypowdered materials but also in the form of different shaped objects.When using shaped objects of pyrogenic mixed oxides or forming suchshaped objects directly before the hydrothermal reaction, a subsequentagglomeration step is not necessary. The addition of catalyticallyinactive binders is also superfluous.

[0033] A further advantage of shaped objects of crystalline microporousand mesoporous metal silicates obtainable according to the invention isthat they can be separated more easily from liquids filtration thanunshaped catalysts, thereby facilitating their use as suspensioncatalysts. As pyrogenic mixed oxides are easy to shape, for instanceinto spheres, extrudates, pellets or tablets and the shape remainsessentially unchanged in the process according to the invention, saidprocess directly produces suitable shaped objects for use as catalystsin fixed bed reactions.

[0034] Although it is know from EP 0 311 983 B that coprecipitatedTiO₂—SiO₂ material can be used for the preparation of titaniumsilicates, the copreciptates to be used are very porous products. It wastherefore surprising that crystalline microporous and mesoporous metalsilicates are easily obtainable by using pore-free pyrogenic mixedoxides such as those used in the process according to the invention.

[0035] As such, preferably in the form of shaped objects, thecrystalline microporous and mesoporous metal silicates obtainableaccording to the invention are used as catalysts. Titanium silicalitesand other aluminum-free products are particularly suitable as catalystsfor oxidation reactions with hydrogen peroxide or organichydroperoxides. Examples are the use of titanium silicalite-1 as acatalyst for the reaction of olefins, i.e., propene, with hydrogenperoxide to give epoxides (EP 100 119), the reaction of aromatics withhydrogen peroxide to give hydroxyaromatics (DE 31 35 559), the reactionof aliphatic hydrocarbons with hydrogen peroxide to give alcohols andketones (EP 376 453) and the reaction of cyclohexanone with hydrogenperoxide and ammonia to give cyclohexanone oxime (EP 208 311). Titaniumsilicalite-2 is used as a catalyst for the hydroxylation of phenol (J.S. Reddy, S. Sivasanker, P. Ratnasamy, J. Mol. Catal. 71 (1992) p. 373)and for the reaction of cyclohexanone with hydrogen peroxide and ammoniato give cyclohexanone oxime (J. S. Reddy, Reddy, S. Sivasanker, P.Ratnasamy, J. Mol. Catal. 71 (1992) p. 383) . Titanium beta-zeolite canbe used as a catalyst for the reaction of olefins with hydrogen peroxideor organic hydroperoxides to give epoxides (A. Corma, P. Esteve, A.Martinez, S. Valencia, J. Catal. 152 (1995) p. 18 and EP 659 685).

[0036] The following examples serve to illustrate the present invention.

EXAMPLE 1

[0037] Preparation of Titanium Silicalite-1 Powder

[0038] 137.0 g of tetrapropylammonium hydroxide solution (40 wt. %) and434.2 g of deionized water are placed in a polyethylene beaker and 111.1g of pyrogenic silicon-titanium mixed oxide containing 3.0 wt. % of TiO₂are added, with stirring. The resulting synthetsis gel is first aged forfour hours at 80°C., with stirring, and then crystallized in anautoclave for 24 hours at 175°C. The solid obtained is separated fromthe mother liquor by centrifugation, washed with three times 250 ml ofdeionized water, dried at 90°C. and calcined in an air atmosphere forfour hours at 550°C. The yield is 98.3 g.

[0039] The X-ray diffraction diagram of the catalyst prepared in thisway shows the diffraction pattern typical of the MFI structure, and theIR spectrum shows the band at 960 cm⁻¹ characteristic oftitanium-containing molecular sieves. Wet chemical analysis gives atitanium content of 2.3 wt. % of TiO₂. The DR-UV-Vis spectrum also showsthat the sample is free of titanium dioxide.

EXAMPLE 2

[0040] Application Example of the Epoxidation of Propylene With HydrogenPeroxide

[0041] 1.0 g of the catalyst prepared according to Example 1 in 300 mlof the methanol is placed in a thermostated laboratory autoclave withgas dispersion stirrer, at 40°C. under a propylene atmosphere, and thesolvent is saturated with propylene under an excess pressure of 3 bar.13.1 g of 30 wt. % aqueous hydrogen peroxide solution is then added allat once, with stirring, and the reaction mixture is kept at 40°C. and 3bar, additional propylene being metered in via a pressure regulator inorder to make up the quantity consumed by the reaction. Samples aretaken at regular intervals via a filter, and hydrogen peroxide contentof the reaction mixture is determined by redox titration with cerium(IV) sulphate solution. The plot of 1n(c/c₀) against the time t, c beingthe measured H₂O₂ concentration at time t and c₀ being the calculatedH₂O₂ concentration at the start of the reaction, gives a straight line.An activity coefficient k of 25.4 min⁻¹ is determined from the gradientof the lines by means of the relationship dc/dt=−k·c·c_(cat), wherec_(cat) is the catalyst concentration in kg of catalyst per kg ofreaction mixture.

EXAMPLE 3

[0042] Preparation of Titanium Silicalite-1 Microgranules

[0043] 800 g of deionized water and 30 g of acetic acid are placed in apolyethylene beaker and 200 g of pyrogenic silicon-titanium mixed oxidecontaining 3.6 wt. % of TiO₂ are added, with stirring. This mixture issheared for five minutes in an Ultraturax stirrer. The resultingsuspension is dried by means of a spray dryer (NIRO-Atomizer model 1638;inlet temperature 380°C.; outlet temperature 102°C.; speed of rotationof the spray disk 15,000 min⁻¹). 20 g of the resulting microgranules,with a mean particle diameter of 30 μm, are impregnated with a mixtureof 20 g of tetrapropylammonium hydroxide solution (40 wt. %) and 20 g ofdeionized water. The impregnated microgranules are charged into anautoclave with a Teflon inliner and crystallized for 24 hours at 175°C.under static conditions. The solid obtained is separated from the motherliquor by centrifugation, washed three times with 100 ml of deionizedwater, dried at 90°C. and calcined in an air atmosphere for four hoursat 550°C. The yield is 17 g.

[0044] The catalyst prepared in this way consists of titaniumsilicalite-1 microgranules.

EXAMPLE 4

[0045] Preparation of Titanium Silicalite-1 Microgranules

[0046] 720.7 g of deionized water and 179.3 g of tetrapropylammoniumhydroxide solution (40 wt. %) are placed in a polyethylene beaker and100 g of pyrogenic silicon-titanium mixed oxide containing 3.6 wt. % ofTiO₂ are added, with stirring. This mixture is sheared for five minutesin an Ultraturax stirrer. The resulting suspension is dried by means ofa spray dryer (NIRO-Atomizer model 1638; inlet temperature 380°C.;outlet temperature 90° C.; speed of rotation of the spray disk 15,000min⁻¹). 20 g of the resulting microgranules, with a mean particlediameter of 30 μm, a loss on drying of 23 wt. % (10 h at 105°C.;corresponds to the water content) and a loss on calcination of 43 wt. %(5 h at 550°C.; corresponds to the water and template content), arecharged into an autoclave with a Teflon inliner and crystallized for 4days at 180°C. under static conditions. The solid is then dried at 90°C.and calcined in an air atmosphere for four hours at 550°C.

[0047] The catalyst prepared in this way consists of titaniumsilicalite-1 microgranules.

EXAMPLE 5

[0048] Preparation of a Titanium Beta-Zeolite Powder

[0049] 435.3 g of tetraethylammonium hydroxide solution (35 wt. %) and236.3 g of deionized water are placed in a polyethylene beaker and 109.6g of pyrogenic silicon-titanium mixed oxide containing 3.0 wt. % of TiO₂is added. The resulting mixture is aged for four hours at 80° C. and,after cooling to room temperature, 12 g of beta-zeolite seed crystalswith an SiO₂/Al₂O₃ ratio of 27 are added. This synthesis gel iscrystallized in an autoclave for 3 days at 150°C., with stirring.

[0050] The solid obtained is separated from the mother liquor bycentrifugation, washed three times, each time with 250 ml of deionizedwater, dried at 90°C. and calcined in an air atmosphere for four hoursat 550°C.

[0051] The X-ray diffraction diagram of the catalyst prepared in thisway shows the diffraction pattern typical of the BEA structure. Wetchemical analysis gives a titanium content of 1.8 wt. % of TiO₂.

EXAMPLE 6

[0052] Preparation of a Mesoporous Titanium Silicate of the MCM-41Structure

[0053] 114.2 of tetramethylammonium hydroxide solution (10% wt. %) isplaced in a polyethylene beaker and 30.0 g of pyrogenic silicon-titaniummixed oxide containing 3.6 wt. % of TiO₂ are added, with stirring. Thismixture is stirred for one hour. A suspension of 29.1 g ofcetyltrimethylammonium bromide (C₁₆H₃₃(CH₃)₃NBr) in 109.2 g of deionizedwater is then added, with stirring, and stirring is continued for 10minutes. The resulting synthesis gel (molar composition: SiO₂: 0.17C₁₆H₃₃(CH₃)₃N⁺:0.26 Me₄NOH:25 H₂O) is crystallized in an autoclave for48 hours at 140°C. under static conditions. The solid obtained isfiltered off and washed with deionized water until the filtrate isneutral. The solid is dried at 90°C. and then calcined in an airatmosphere for four hours at 640°C. The yield is 28 g.

[0054] The X-ray diffraction diagram of the catalyst prepared in thisway shows the diffraction pattern typical of the MCM-41 materials, withd₁₀₀ reflection at 3.60 nm. Examination by sorption analysis withnitrogen at 77 K shows a mean pore diameter of 3.16 nm, a BET specificsurface area of 1040 m² g⁻¹ and a pore volume of 0.89 ml/g. Wet chemicalanalysis gives a titanium content of 4.6 wt. % of TiO₂. The material iscatalytically active in the epoxidation of propene with hydrogenperoxide.

EXAMPLE 7

[0055] Preparation of a Mesoporous Titanium Silicate of the MCM-48Structure

[0056] 114.2 g of tetramethylammonium hydroxide solution (10% wt. %) isplaced in a polyethylene beaker and 30.0 g of pyrogenic silicon-titaniummixed oxide containing 3.6 wt. % of TiO₂ are added, with stirring. Thismixture is stirred for one hour. A suspension of 114.2 g ofcetyltrimethylammonium bromide (C₁₆H₃₃(CH₃)₃NBr) in 435.2 g of deionizedwater is then added, with stirring, and stirring is continued for 10minutes. The resulting synthesis gel (molar composition: SiO₂:0.65C₁₆H₃₃(CH₃)₃NBr:0.26 Me₄NOH :62 H₂O) is crystallized in an autoclave for48 hours at 140°C. under static conditions. The solid obtained isfiltered off and washed with deionized water until the filtrate isneutral. The solid is dried at 90°C. and then calcined in an airatmosphere for four hours at 640°C.

[0057] The catalyst prepared in this way consists of Ti-MCM-48.

EXAMPLE 8

[0058] Preparation of a Boron Pentasil Zeolite

[0059] 800 g of aqueous hexamethylenediamine solution (50 wt. %) isplaced in a polyethylene beaker and 70.7 g of pyrogenic silicon-boronmixed oxide containing 9.5 wt. % of B₂O₃ is added, with stirring. Thismixture is stirred for half an hour and then crystallized in anautoclave for five days at 170°C. The solid obtained is separated fromthe mother liquor by centrifugation, washed three times in 250 ml ofdeionized water, dried at 90°C. and calcined in an air atmosphere forsix hours at 550°C.

[0060] The X-ray diffraction diagram of the catalyst prepared in thisway shows the diffraction pattern typical of the MFI structure. Wetchemical analysis gives a B₂O₃ content of 2.4 wt. %.

EXAMPLE 9

[0061] Preparation of a Boron Silicate of the MCM-41 Structure

[0062] 156.7 g of tetramethylammonium hydroxide solution (10 wt. %) isplaced in a polyethylene beaker and 42.3 g of pyrogenic silicon-boronmixed oxide containing 5.5 wt. % of B₂O₃ is added, with stirring. Thismixture is stirred for one hour. A suspension of 65.5 g ofcetyltrimethylammonium bromide (C₁₆H₃₃(CH₃)₃NBr) in 576.5 g of deionizedwater is then added, with stirring, and stirring is continued for 10minutes. The pH is adjusted to 11.5 by the addition of dilute sulphuricacid. The resulting synthesis gel is crystallized in an autoclave for 48hours at 140°C. under static conditions. The solid obtained is filteredoff and washed with deionized water until the filtrate is neutral. Thesolid is dried to 90°C. and then calcined in an air atmosphere for fourhours at 540°C.

[0063] The X-ray diffraction diagram of the catalyst obtained shows thediffraction pattern typical of the MCM-41 materials. Examination bysorption analysis with nitrogen at 77°K. shows a mean pore diameter of2.83 nm, a BET specific surface area of 1060 m² /g and a pore volume of0.89 ml/g.

EXAMPLE 10

[0064] Preparation of a Zirconium Silicalite-1 Powder

[0065] 62.4 g of tetrapropylammonium hydroxide solution (40 wt. %) and229.8 g of deionized water are placed in a polyethylene beaker and 57.4g of pyrogenic silicon-zirconium oxide containing 3.0 wt. % of ZrO₂ areadded, with stirring. The resulting synthesis gel is then crystallizedin an autoclave for 24 hours at 175°C. The solid obtained is separatedfrom the mother liquor by centrifugation, washed with three times 250 mlof deionized water, dried at 90°C. and calcined in an air atmosphere forfour hours at 550°C.

[0066] The X-ray diffraction diagram of the catalyst obtained shows thediffraction pattern typical of the MFI structure. X-ray fluorescenceanalysis gives ZrO₂ content of 1.0 wt. %

EXAMPLE 11

[0067] Preparation of a Zirconium Silicate of the MCM-41 Structure

[0068] 114.2 g of tetramethylammonium hydroxide solution (10 wt. %) areplaced in a polyethylene beaker and 30.0 g of pyrogenicsilicon-zirconium oxide containing 3.0 wt. % of ZrO₂ is added, withstirring. This mixture is stirred for one hour. A suspension of 29.1 gof cetyltrimethylammonium bromide (C₁₆H₃₃(CH₃)₃NBr) in 109.2 g ofdeionized water is then added, with stirring, and stirring is continuedfor 10 minutes. The resulting synthesis gel is crystallized in anautoclave for 48 hours at 140°C. under static conditions. The solidobtained is filtered off and washed with deionized water until thefiltrate is neutral. The solid is dried to 90°C. and then calcined in anair atmosphere for four hours at 640°C.

[0069] The X-ray diffraction diagram of the catalyst obtained shows thediffraction pattern typical of the MCM-41 materials with a d₁₀₀ value of3.25 nm. Examination by sorption analysis with nitrogen at 77 K shows amean pore diameter of 2.4 nm, a BET specific surface area of 860 m²/gand a pore volume of 0.59 ml/g.

[0070] Further variations and modifications of the foregoing will beapparent to those skilled in the art and intended to be encompassed bythe claims appended hereto.

[0071] German priority application 196 24 340.8 is relied on andincorporated hereby reference.

We claim:
 1. A binder-free shaped objected selected from the groupconsisting of microporous and mesoporous metal silicates, obtained bythe hydrothermal reaction of a silicon and metal source in the presenceof a template, wherein a pyrogenic metal-silicon mixed oxide is thesilicon and metal source.
 2. The binder-free shaped object according toclaim 1 wherein the crystalline microporous and mesoporous metalsilicates are represented by the composition(SiO₂)_(1−x)(A_(m)O_(n))_(x)   (Ia),(SiO₂)_(1−x)((A_(m)O_(n))_(1-y)(A′_(m),O_(n),)_(y))_(x)   (Ib) or(SiO₂)_(1−x)(M_(r)A_(m)O_(n),)_(x)   (II) in which x is a number from0.0001 to 0.25; y is a number greater than 0 and less than 1; A and A′are a metal of valency p selected from the group consisting of B, Al,Ga, In, Ge, Sn, Pb, and subgroups 3 to 8 of the Periodic Table ofElements; M is a cation of valency q selected from the group consistingof alkali metals, alkaline earth metals, H⁺, NH₄ ⁺and N(alkyl)₄ ⁺ m, m′,n, n′, n″ and r are the number of atoms, where: m·p=2n and m′·p=2n′ andm·p+r·q=2n″, wherein a pyrogenic mixed oxide of composition (Ia) or (Ib)is used and the cation M of formula (II) is incorporated via thetemplate or via alkali metal or alkaline earth metal hydroxide presentin the hydrothermal reaction.
 3. The binder-free shaped object accordingto claim 1 wherein said pyrogenic metal-silicon mixed oxide is preparedby flame hydrolysis.
 4. The binder-free shaped object according to claim1 wherein said pyrogenic mixed oxide is selected from the groupconsisting of (SiO₂)_(1−x)(TiO₂)_(x), (SiO₂)_(1−x)(Al₂O₃)_(x),(SiO₂)_(1−x)(B₂O₃)_(x), (SiO₂)_(1−x)(V₂O₅)_(x) and (SiO₂)_(1−x)(ZrO₂)_(x).
 5. The binder-free shaped object according to claim 4 whichis (SiO₂)_(1−x)(TiO₂)_(x) .
 6. The binder-shaped object according toclaim 1 wherein said template is an amine having one or more aminogroups, an amino alcohol or a tetrasubstituted ammonium compound.
 7. Thebinder-free shaped object according to claim 1 wherein said template isused in an amount of 0.05 to 2.0 mol per mol of SiO₂ in the mixed oxide.8. The binder-free shaped object according to claim 1 further comprisingcarrying out the hydrothermal reaction for the preparation ofmicroporous metal silicates at a temperature from 100 to 220°C.
 9. Thebinder-free shaped object according to claim 1 further comprisingcarrying out the hydrothermal reaction for preparation of microporousmetal silicates at a temperature from 150 to 190°C.
 10. The binder-freeshaped object according to claim 1 wherein the preparation of mesoporousmetal silicates is carried out at a temperature from 50 to 175°C. underat least autogenous pressure.
 11. A process for catalytic oxidationreactions, wherein a catalyst is present corresponding to an Al-freemetal silicalite defined in claim 1 .
 12. The process according to claim11 wherein the catalyst is (SiO₂)_(1−x)(TiO₂)_(x).
 13. A process for theoxidation of an olefin wherein a catalyst is present, said catalystbeing the binder-free shaped object of claim 1 .
 14. The processaccording to claim 13 wherein the catalyst is (SiO₂)_(1−x)(TiO₂)_(x).15. The process according to claim 11 wherein propene is oxidized withhydrogen peroxide to give the corresponding epoxide.
 16. The processaccording to claim 12 wherein propene is oxidized with hydrogen peroxideto give the corresponding expoxide.
 17. A process for preparing ahydroxy aromatic compound comprising reacting an aromatic compound withhydrogen peroxide or an organic hydroperoxide in the presence of abinder-free shaped object according to claim 1 .
 18. A process forproducing an alcohol or ketone comprising reacting an aliphatichydrocarbon with hydrogen peroxide or an organic hydroperoxide in thepresence of a binder-free shaped object according to claim 1 .
 19. Theprocess according to claim 18 , wherein a ketone is converted to anoxime by reacting with hydrogen peroxide and ammonia.
 20. A process forthe catalytic epoxidation of an olefin with hydrogen peroxide as theoxidant comprising carrying out the epoxidation in the presence of acatalyst which is a crystalline microporous titanium silicate of thecomposition (SiO₂)_(1−x)(TiO₂)_(x) in which x is a number from 0.001 to0.2 wherein a pyrogenic silicon-titanium mixed oxide is reacted withtetraalkylammonium hydroxide template in a hydrothermal reaction at atemperature from 100 to 220°C., and wherein the pyrogenicsilicon-titanium mixed oxide is shaped to microgranules by a spraydrying process prior to the hydrothermal reaction and a crystallinemicroporous titanium silicate in the form at microgranules is formed.21. The process of claim 20 , wherein the olefin is propene.